fix: package.json & yarn.lock to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BABELHELPERS-9397697

Author: snyk-bot

package.json

@@ -11,7 +11,7 @@
     "lint": "next lint"
   },
   "dependencies": {
-    "@mdx-js/loader": "^1.6.22",
+    "@mdx-js/loader": "^2.0.0",
     "@next/mdx": "^11.1.0",
     "next": "12",
     "react": "^17.0.2",